Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a progressive loss of cognitive abilities and by characteristic neuropathological features comprising deposits of amyloid beta (Aβ) peptide, neurofibrillary tangles and neuronal loss in several regions of the brain (Hardy and Selkoe, Science 297: 353, 2002; Mattson, Nature 431: 7004, 2004. Cerebral amyloid deposits and cognitive impairments very similar to those observed in Alzheimer's disease are also hallmarks of Down syndrome (trisomy 21), which occurs at a frequency of about 1 in 800 births.
The Aβ peptide arises from the amyloid precursor protein (APP) by proteolytic processing. This processing is effected by the cooperative activity of several proteases named α-, β- and γ-secretase and leads to a number of specific fragments of differing length. The amyloid desposits consist mostly of peptides with a length of 40 or 42 amino acids (Aβ40, Aβ42). This also includes, in addition to human variants, isoforms of the amyloid β(1-42) protein present in organisms other than humans, in particular, other mammals, especially rats. This protein, which tends to polymerize in an aqueous environment, may be present in very different molecular forms. A simple correlation of the deposition of insoluble protein with the occurrence or progression of dementia disorders such as, for example, Alzheimer's disease, has proved to be unconvincing (Terry et al., Ann. Neurol. 30: 572-580, 1991; Dickson et al., Neurobiol. Aging 16: 285-298, 1995). In contrast, the loss of synapses and cognitive perception seems to correlate better with soluble forms of Aβ(1-42) (Lue et al., Am. J. Pathol. 155: 853-862, 1999; McLean et al., Ann. Neurol. 46: 860-866, 1999).
None of the polyclonal and monoclonal antibodies which have been raised in the past against monomeric Aβ(1-42) have proven to produce the desired therapeutic effect without also causing serious side effects in animals and/or humans. For example, passive immunization results from preclinical studies in very old APP23 mice which received a N-terminal directed anti-Aβ(1-42) antibody once weekly for 5 months indicate therapeutically relevant side effects. In particular, these mice showed an increase in number and severity of microhemorrhages compared to saline-treated mice (Pfeifer et al., Science 298: 1379, 2002). A similar increase in hemorrhages was also described for very old (>24 months) Tg2576 and PDAPP mice (Wilcock et al., J Neuroscience 23: 3745-51, 2003; Racke et al., J Neuroscience 25: 629-636, 2005). In both strains, injection of anti-Aβ(1-42) resulted in a significant increase of microhemorrhages.
WO 2004/067561 refers to globular oligomers (“globulomers”) of Aβ(1-42) peptide and a process for preparing them. WO 2006/094724 relates to non-diffusible globular Aβ(X−38 . . . 43) oligomers wherein X is selected from the group consisting of numbers 1 . . . 24. WO 2004/067561 and WO 2006/094724 further describes that limited proteolysis of the globulomers yields truncated versions of said globulomers such as Aβ(20-42) or Aβ(12-42) globulomers. WO 2007/064917 describes the cloning, expression and isolation of recombinant forms of amyloid β peptide (referred to hereafter as N-Met Aβ(1-42)) and globulomeric forms thereof. The data suggest the existence of an amyloid fibril independent pathway of Aβ folding and assembly into Aβ oligomers which display one or more unique epitopes (hereinafter referred to as the globulomer epitopes). Since globulomer epitopes were detected in the brain of AD patients and APP transgenic mice and the globulomer specifically binds to neurons and blocks LTP, the globulomer represents a pathologically relevant Aβ conformer. It has been found that soluble Aβ globulomer exert its detrimental effects essentially by interaction with the P/Q type presynaptic calcium channel, and that inhibitors of this interaction are therefore useful for treatment of amyloidoses such as Alzheimer's disease (WO 2008/104385).
Antibodies which selectively bind to such globulomeric forms of Aβ have been described in WO 2007/064972, WO 2007/062852, WO 2008067464, WO 2008/150946 and WO 2008/150949. For instance, several monoclonal antibodies known from WO 2007/062852 and WO 2008/150949 specifically recognize Aβ(20-42) globulomer.
There exists a tremendous, unmet therapeutic need for the development of biologics such as Aβ binding proteins that prevent or slow down the progression of the disease without inducing negative and potentially lethal effects on the human body. Such a need is particularly evident in view of the increasing longevity of the general population and, with this increase, an associated rise in the number of patients annually diagnosed with Alzheimer's disease or related disorders. Further, such Aβ binding proteins will allow for proper diagnosis of Alzheimer's disease in a patient experiencing symptoms thereof, a diagnosis which can only be confirmed upon autopsy at the present time. Additionally, the Aβ binding proteins will allow for the elucidation of the biological properties of the proteins and other biological factors responsible for this debilitating disease.